Process of extracting zinc from its ores or compounds.



E. E. WATTS. PROCESS 0F BXTRAGTING ZINC BRGM ITS omas 0R COMPOUNDS'.

APPLICATION FILED NOV. Z0. 1913,v I

Patented Sept. 22. 1914.

nvcmoz WATTS- UNTTED sTATEs PATENT omiten.

ERNESI ESTRAM WATTS, OF .KINGSTOI ONTARIO, CANADA.

PROCESS OF EXTRACTING ZINC FROM ITS CRES R COMPOUNDS.

Specification of Letters Intent.. y Patented Sept. 22, 1914.

Application med November ao, i913. serial N6. scalza skilled inthe art to which it appertains to make and use the same.

-zinc from' eres or compounds containingit l ably produce zinc.

This invention relates to a process for extracting zinc from'l its ores;

The object of the b invention is to obtain inI a cheap and convenient manner'which is lespecially adapted for use i'n certain localities;

In the accompanying drawings are shown one form of apparatus used in connection with this improved process, Figure 1 representing a planl view thereof: Fig. 2 an end elevation partly in section; and Fig. 3 a side 25 elevation partly in section.

In the standard method of extracting zinc from ores or compounds by distillation, the most -skilful attentionis necessary, and then losses of up to 25 per cent. of the metal occur. There is also `considerable wear and tear upon the retorts and furnaces. Moreover, zinc ores or products lower than 40 per cent. in zinc cannot usually be treated at a. profit by this method. F or these reasons, zinc. mines in localities situated at a distance from fuel supplies and suitablenclays for retort manufacture are unable to profit- Furthermore, for the following reasons, the recoveryv of zinc by electrolytic methods has hitherto been but slightly successful, "(1)-the power consumption necessary to deposit a strongly electropositive metal like zinc from aqueous solution by using insoluble anodes, is high; (2) great difficulty hasbeen experienced inobtaining a good cathodic deposit of zinc; (3)

great difficulty hasbeen experienced inV ob-` taining an electrolyte of 'the necessary con-v stant composition and purity. By myl invention, I have overcome most of these dis,- advantages, and very largely corrected the others and I propose to produce a compound or product high in zinc and to then introduce this compound or product in the form of a paste into an electrolytic bath of a nearly l'saturatedA solution of a zinc salt in anode compartments of the said bath. Upon the passage of' a suitable current zinc will deposit upon the cathodes, and the acid lib erat'ed'by the electrolysis will be constantly used up in dissolving zinc from the compound 01' product in the anode compartments inthe form in which it already exists in the bath.. The concentration and composition of the electrolyte will thus be maintained constantly-at the conditions yfor high current etli'cie'ncy and good cathode deposit. By the aid of eiicient circulation, and the addition of certain substances which I shall later specify, high current efficiency may be further assured and the character of the deposit improved. -The various steps in this system of zinc extraction are later more particularly described.

In the form of apparatus herein shown a plurality of tanks 1, 2 and 3 are shown arranged in serieswith circulation pipes as .4 connecting the adjacent'tanks, the circulation taklng place by gravity as each tankl is 'disposed slightly lower than its predecesser in the series. Cathodes 5 are shown extending transversely of each tank with anodes (ik alternating therewith. Each of the anodes is shown disposed in a compartment 7 which compartments are composed of any suitable material which will allow the passage of the liquid of the bath therethroughpbut'will prevent the passage of the past-.e dispo-sed therein as will be hereinafter described;A The points of c ontact between the anodes and cathodes are shown at 8 and 9 respectively which are herein shown in the form oflugs or projections at the tops of ythe plates forming the anodes and cathodes,

these lugs being shown `in Fig. 2 as projecting over the side of the tank and holding the plates suspended. Contact between the plates and the tank is prevented by insulationbetween the legs andthe walls of the tank except at the points indicated. The stipple shown at 10 in the compartments 7 represent the paste which is employed in the process as will be hereinafter described.

Any suitable method may be employed to obtain the compounds or products high in zinc for lintroduction into the eletrolytic bath, several instances are given below, to Wit: From zinc ores amenable to concentration, I may concentrate bv ore-dressing methods suited to the particular ore and so obtain a concentrate or' product high in zinc. This concentrate must then be roasted until practically free from sulfur as sulfd and sulfate of zinc and then introduced into the bath in the manner to be described. Zinc products or by-products not amenable to concentration, such as blue powder, or impure zinc oxid, free from objectionable impurities that would tend to foul the bath, such as sulfids and sultes, are suitable products for introduction into the bath. In case of the presence of objectionable impurities, it will be necessary to free the product from these if possible before charging to the bath.

, Complex lead zinc'ores may be treated in the following manner to obtain a compound or product suitable forcharging to the bath, to wit: First the ore is roasted if found necessary and then the zinc contents in the form of oxid volatilized in any suitable manner fro-m the roasted or unroasted ore. l

A further method of treating complex lead zinc ores high in sulfur in order to obtain a compound or product suitable for charging to the electrolytic bath, is as follows: The ore is first finely crushed, roasted in an oxidizing atmosphere, and the roast leached with sulfurousA acid. The zinc dissolves as zinc bisulte, and from the solution I precipitate t-he zinc as zinc `,monosulfite by expelling the sulfur dioxid from the solution by boiling. I then remove the zincv monosulfite precipitate and roast it to remove all combined and uncombined sulfur, so producing an impure zinc oxi`d' product suitable for charging to the electrolytic bath.

It is known that zinc sulfate forms in roasting blende. This is dissolved upon leaching with sulfurous acid and cannot be precipitated by boiling. I have also found that if the roasting is performed at a temperature at about 750 C. or below, that in addition to some zinc sulfate, someiron sulfate also remains undecomposed, and, upon leaching and attempting tfo precipitate the zinc by boiling, up to 50% of the zinc in solution will not precipitate but remains in solution of sulfate. It is also known that in roasting blende at a temperature exceeding 950" C., that zinc and iron are liable to combine to form a compound known as zinc ferrite which is insoluble in sulfurous acid.

I avoid these difficulties by carrying on the roasting operation at a temperature of about 700 C. to 800 C. until the sulfur is largely removed and' then at a temperature of about 900 C. to 950 C. until the roast is completely finished., Then, the zinc and iron sulfates are practically completely decomposed, and but little zinc ferrite is formed. I find that the roasts that are finished at a high temperature are diilicult to extract by means of sulfurous acid for there appears to be an insoluble film inclosing the grains of the roast. This difficulty I overcome by reinding the roast to afine powder. This l nely pulverizecl roast I then leach with sulfurous'acid in a suitable apparatus in which the sulfur dioxid of the roaster gases is dissolved in water under slight pressure. I also propose utilizing the sulfur dioxid gas generated by the precipitation of the solution and by the roasting ofthe precipitate in the same or a similar apparatus. The zinc from the roast goes into solution in sulfurous acid as zinc bisulite.- Limepresent in -the ore will also go intosolution., y i

The ratio of solution to ore varieswith the amount of zinc in the ore, and in general the more concentrated the` solution the greater is the ease vwith which the zinc is precipitated from it. A (Vith a thirty per cent. zinc ore I have obtained excellent results using six parts of solution to one of ore.)` 4

Having obtained the zinc in solution, the

' residue, containing most of the lead, lron,

and precious metals .0f the original ore, is separated from the solution by decantation, or filtration, or both. Having precipitated the zinc monosulte, I propose to first cool the solution, and remove the precipitate by de cantation and filtration, for I have found that, if the solution is not first cooled, the zinc monosultite willci'ystallize out of the solution into the pores of the filtering medium and ,so stop the operation. The precipitate obtained in this manner I propose to roast at a temperature between' 800' C. and 10O0 C. in .an oxidizing atmosphere. As the preclpltate roasts very readily I have found that in about two hours, without the `addition of any other substances, that I can obtain a product practically free from combined or uncombined sulfur, and thus a-product'suitabl for charging to the electrolytic tanks. The solution from the precipitation of the zinc monosulfite will contain some iron which will settle out from the solution after standing twenty-'four hours. The clear solu' tion can then be decanted oli". Zinc sulfate will gradually accumulate in these solutions as they are used and re-used and these solutions may be freed from zinc, and the zinc recovered, by treating the solutions with some cheap precipitant such as soda ash or lime. v

Having obtained products or compounds of zinc suitable for changing` to the electrolytic tanks, these compounds or products are mixed to a thin paste with a solution of zinc sulfate and the paste charged to the electrolytic tanks, and treated in a man ner to be described. It has been found that if the products or compounds are charged to the tanks without mixing them to a thin paste, they will cake, and consequently the zinc is thoroughly extracted from the exterior only of the cake. The compounds or products are charged to the bath to the compartments? It vthe anodes after mixing them to a thin paste with a solution of zinc sulfate. These compartments are simplyv portions 0f the tank surrounding the anodesv partitioned off by any suitable material which will allowthe passage of the liquid of the bath, but prevent thev passage of the paste fromjthe compartments. Thus the bath is kept free from solids and constantly at the composition and. concentration necessary for high current eiiciency and good cathode deposit. f 'l It. is known, that in the electrolysis of a isolation of zinc sulfate, that zinc is deposited at .the cathode, and sulfuric acid generated at the anode `by secondary reaction. If this acid is noty removed in some manner, after the acid in the bath reaches a certain low concentration, hydrogen and not zinc is liberatedat the cathode. Thus,

by this'method of introduction-of a compound 'or product containing zinc at the anode, the acid 'is immediately #consumed and the concentration of `the solution ivith lrespect to zinc kept constant. At the y of-less electro-positive metals such as iron.

Thus, in the system of zinc extraction, I obtainl high current eiciency and good cathode deposits, and maintain the solution constantly at the concentration and composition necessary for obtaining these. As the depleted residue in the anode compartments is removed, fresh material is added, and the process is thus continuous. The

residue is separated from the solution, and

the solution returned tothe tanks.

During the process there is some loss of solution due to 'evaporation and losses in handling. This loss may be corrected by the addition of fresh solution,or by maintaining the volume of the solution constant by the addition of Water, and adding the necessary amount of zinc sulfate. This zinc sulfate may be obtained by` controlling the conditions during the roasting of the va: rions zinc and sulfur holding products, or, may be obtained by exposing the'zinc monosulite precipitateI from the sulfurous yacid leach to the atmosphere for a few Weeks. The z'inc monosulfite is then practically completely oxidized to sulfate and this zinc sult'ate may be charged'to the bath. It is of 4` course inadvisable to have large quantities of zinc sulfate added to the bath in the usual addition of the pastes, and I preferably add just suiiicient zinc sulfate, to make up for.

unavoidable losses. If large amounts of zinc sulfate' were added in the pastes, the

acid generated through electrolysis could notbe neutralized. in the manner above described.

In the anode 'compartments insoluble anod'es of lead are used and these in time bezinc sulfate keptconstantly at a concentration oftwelve per cent. or over of zinc in -the manner above described, is'preferably used, -but a -zinc chlorid solution may be used if desired.' 'Y I have vfound that the presence of such substances as gelatin, glue, starch, or sugar, in the bath improve the character of the' zinc deposit tending to make it more dense and compact.

` \In this systemy of'zinc extraction, the elec-r trolytic ytanks shown at 1,2'and 3 are preferably 'arranged in series with the electrodes in each tank in' parallel, and one or two tanks in the series preferably having no current passing therethrough, but in which the anode compartments thereof remain charged. Thus, the solution during circulation has additional opportunity to come in contact with the contents of the anode compartments, and, at any time, any tank may v be thrown out of the circuitfor purposes of cleaning, repairing orv removing the `catliodes, Without interferin of the circuit, the extra tan tuted.

During the electrolysis I nd that I can obtain good results Withcurrent densities at the cathodes of from 2 amps. per sq. dm. to 5 amps. per sq. dm., or 18 amps. per sq. ft. to 45 amps. per sq. ft., and under good conditions, the voltage corresponding to these current densities Will vary from 3.5 volts to six volts, and a current density of about 2.5 amps. per sq. dm. should be maintained With a difference of potential of 3.5 volts between electrodes.

v The action of sulfurous acid upon oxid of zinc is Well known, as is also the possibility of theelectro-deposition of zinc from a zinc sulfateor zinc chlorid solution, but, the combination and modifications of these processes I-clairn'ajs my invention.

i What I claim-as new is:

l. A process of extracting zinc which comprises mixing a material containing a high-percentage of`zinc in a non-elemental condition with a solution of zinc sulfate relat"vely free from dissolved iron compounds, improportions to form a thin paste, chargbeing substiwith the rest passing a suitable electric currentthrough said cell, whereby the zinc is deposited at the cathodes.

2. A process of product high in zinc existing in a non-elemental co'ndition with a suiiicient quantity of a solution of a zinc salt tosform a paste, said solution being substantially free from iron, charging said paste into the anodel being kept separate from the liquid sur-l rounding tlie cathode. l

3. A process of extracting zinc electrolytically which comprises mixing impure zinc oxid substantially free from elemental zinc With a suiicient amount of a solutionof zinc sulfate to form a paste, said solution of zinc sulfate being relatively free from dissolved iron compounds, introducing said paste into the anode compartment of an elec- 'extracting zinc electro-` lytically which comprises first mixing atrolyticfoell -entaining an electrolyte com;- prisln'g a' solutionofzinc sulfate, .passing a current. ofv electricity through said cell, thereby depositing metallicA zinc at the cathode;

4. A process of separating metallic zinc, which comprises mixing a material contain'- in'. zinc in a non-elemental conditionwith a su cient amount of a solution of `zinc'sulfate. to form thin paste, introducing said paste into the anode compartments of an electrolytic cell containing an electrolyte consisting of a solution of `zinc sulfate, containing aboutl'; of zinc, said electrolyte also containing an organic material capable of rendering the zinc deposit dense and. comflo pact, and passing a suitableelectric current through said cell, whereby zinc is deposited, at thecathodes. A

In testimony whereofI have hereunto set my hand in presence of two subscribing Wit- Y nesses.

Witnesses:

GEO. H. SMYTmza;

ANNA HANLON.

'aNEsT ESTRAM WATTS. 

